Inspection and repair of the hottest large storage

Detection and repair of large storage tanks

large storage tanks are basically welded from steel plates. With the continuous development of production technology, the large-scale storage tanks and multi tank clusters lead to the concentration of hazards and the severity of disasters. For example, in a liquefied natural gas plant in umm said, Qatar, a refrigeration propane storage tank with a volume of 260000 barrels (the temperature is -43 ℃, and the storage capacity is about 90% of the volume). Due to problems in manufacturing and welding quality, a weld crack liquid propane leakage accident occurred in the process of use, with a leakage of about 14000 barrels (2226m3). As a result, it was forced to stop production in an emergency. The cans made of aluminum foil had poor transparency. After taking various measures, the storage tanks were welded and repaired. However, there are still problems in the repair quality and the inspection and evaluation methods after the repair are backward, so the problem can not be found, resulting in serious rupture after being put into operation again for 1 year, a large amount of liquid propane overflows, crosses the liquid dike and flows into the refrigeration area, resulting in a major fire accident. The fire is fierce and has not been reduced for 3 days. The fire can be put out after the same kind of cement has been put into a tank for 8 days every day. The accident also caused serious damage to a nearby refrigeration propane storage tank with a volume of 125000 barrels (19873 m3) and most facilities in the refrigeration area, with an economic loss of about US $121 million. From this accident case, we can see how important it is to detect and repair large storage tanks, which must be paid great attention to, and do a good job in the detection and repair of large storage tanks to ensure safe operation and prevent accidents

due to the comprehensive influence of complex factors such as the geological condition of the storage tank base, the types of stored items, operation, management and maintenance, the performance of the storage tank will be degraded after years of use, which may lead to accidents. For this reason, all materials in the storage tank must be transferred and discharged regularly, and then replaced and cleaned. After meeting the requirements, the storage tank shall be comprehensively inspected according to the specified standards, and the storage tank shall be inspected with nondestructive testing methods and means. On this basis, the inspection and testing results report shall be written, and the storage tank shall be repaired accordingly as needed to ensure the safe operation of the storage tank and avoid accidents

according to the relevant regulations of Japan, storage tanks with a volume of more than 1000 m3 must be regularly inspected, tested and repaired. Confirm whether the inspected storage tank meets the technical standards. If it does not meet the technical requirements, repair it until it meets the requirements. From the perspective of repair, it is mostly caused by the development of corrosion and welding defects, and the amount of bottom plate repair is more than twice that of side plate repair. From the point of view of the repair content, it mainly includes the replacement of original plates, the repair of clad plates and welds in 2013

bottom plate repair. The bottom plate repair caused by corrosion is about 80% - 90%, and the vast majority of them are local plate replacement. Although there are large areas or even all replacement, there are few. However, as people consider more and more safety, the replacement area is also gradually increasing. For the storage tank built in the early stage, due to less consideration of the base, when the hydrostatic test and calibration are carried out after the completion, the base sinks locally, causing the deformation and uneven corrosion of the bottom plate, and the joint weld between the bottom plate and the side plate is damaged. Therefore, while the bottom plate is repaired, the base of the storage tank is transformed, mostly using quartz sand or oil sand or asphalt materials, the bottom plate is made of thicker steel plate materials, and the welding method is lap welding

side plate repair. Because the environment of the side plate is different from that of the bottom plate, the repair amount of the side plate is much less than that of the bottom plate, and most of them are concentrated in the lowest section of the side plate. The reason for the repair is that the point corrosion causes small-area damage. The repair method is mostly surfacing repair, and local side plate replacement and cover plate repair are less. The repair of the position change of the oil inlet and outlet openings of the storage tank is also a common repair of the side plate, which has a small area and limited scope

weld repair. Due to the low welding quality during the construction of storage tanks, after a period of application, the weld defects become serious. At this time, the faulty weld must be repaired. The weld repair caused by welding defects accounts for more than 50% of the whole weld repair. After long-term application of the storage tank, some welds have problems due to corrosion, deformation, stress and other reasons. At this time, they must also be repaired. The most repaired part of the weld is the bottom plate of the storage tank, accounting for about 70% - 80% of the total weld repairs, and the length of the repaired weld is larger than the original weld. The position with the largest weld repair length is at the joint between the side plate and the inner side of the bottom plate. The inner weld repair is much more than the outer weld repair

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